Method of dyeing anodized aluminum articles



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3,092,523 METHOD OF DYEENG ANODIZED ALUMINUM ARTICLES Howard A. Fromson, Rogues Ridge Road, Weston, Conn. No Drawing. Filed Apr. 14, 1961, Ser. No. 102,948

7 Claims. (Q1. l486.1)

Thepresent invention relates to a method of dyeing, sealing and/or protecting the anodized surface of an aluminum article.

Colored aluminum articles are conventionally produced by anodizing the articles to form a porous anodic coating thereon of aluminum oxide, dyeing the anodized coating with a dye in a dye bath, rinsing the colored articles and then sealing the dyed coating to render it nonabsorptive by immersing in hot water, a step which converts the aluminum oxide to aluminum oxide monohydrate. Where it is desired to leave one part of the article undyed, it is the common practice to mask this part with a water insoluble substance such as asphaltum, to prevent contact of this part with the dye. Where two colors are desired, it is the practice to mask part of the anodized surface with the water insoluble substance, dye and seal the rest of the surface, remove the mask, mask the dyed part of the surface and dye and seal the part of the surface from which the mask has been removed. This requires two separate masking steps, two separate dyeing steps, and two separate sealing steps.

One object of the present invention is to provide a new and improved method for treating the anodized surface of an aluminum article to dye, seal and/or protect said surface.

Another object of the present invention is to provide a new and improved method of effecting multi-color dyeing of anodized aluminum with minimum of steps and with maximum of simplicity.

The present invention is predicated on the utilization I of the unique characteristics of certain cellulose ethers and especially methylcellulose. Certain cellulose ethers and especially methylcellulose, with the proper degree of substitution, are soluble in cold water but are insoluble in hot water and form semi-solid gels when heated. The gelation temperature of such cellulose ethers as methylcellulose depends both on the concentration of methylcellulose in the solution and the degree of substitution of the alkyl groups therein to form the alkoxyl radicals. For example, by selecting the proper concentration of methylcellulose having the proper degree of substitution, an aqueous solution of methylcellulose may be produced which is in liquid or semi-liquid or paste form at room temperature according to the desired mode of application but which is a semi-solid gel and insoluble at a temperature above about 115 F.

In accordance with certain features of the present invention, the cellulose ether having the characteristics described, and especially methylcellulose, is formed with a concentration as low as 1% into a water solution and is applied to a predetermined part of the anodized surface of an aluminum article to form a coating thereon. This coating is then heated to the temperature above the gelation point of the methylcellulose to convert the coating into a water-insoluble mask on said surface. This operation may be employed to protect the anodized surface during storage or transportation and/ or may be employed in conjunction with a dyeing step and/ or sealing step.

In accordance with one specific embodiment of the present invention, after the anodized surface has been coated with the solution of methylcellulose and heated above the gelation point of the methylcellulose, the uncoated part of the anodized surface is dyed. The methylcellulose in this embodiment of the invention serves as a 3,092,523 Patented June 4, 1963 mask delineating sharply the dyed area and the masked area and can be easily washed off in water at room temperatune.

More specifically, the embodiment of the process described can be carried out by forming a viscous aqueous solution of methylcellulose at room temperature and by applying this solution in any suitable manner, as for example, by printing, painting or rolling onto the anodized surface of the aluminum article following a predetermined pattern. With a less viscous aqueous solution of methylcellulose, this solution can be sprayed on. The aluminum article treated as described is then submerged in a standard aqueous dye bath heated to the proper dyeing temperature, which is usually between and F. but which in any case is at least in the gelation range of the methylcellulose. The dye bath is preferably below the sealing temperature of the aluminum, which is between 170 and 212 F. The temperature of the dyeing bath causes the methylcellulose solution to gel and to form an insoluble mask over the covered area of the aluminum article, preventing liquid from the dye bath from reaching the masked areas, while the unmasked areas of the anodized aluminum surface are dyed by this bath. After removal from the dye bath, washing of the aluminum article in water at room temperature or at some other temperature at which the methylcellulose is soluble in water will dissolve and remove the methylcellulose mask. The surface of the aluminum article can then be sealed by immersion in hot water above 170 F. The resulting sealed surface will exhibit a two-tone predetermined pattern of dyed and undyed areas.

The aqueous cellulose ether solution applied to an anodized surface of an aluminum article, when thermally gelated, may serve either as a means for masking certain areas of the article during dyeing as described, or as a means of protecting certain areas of the article during storage and/or transportion, against marn'ng.

As another feature of the present invention, it has been determined that a water solution of certain cellulose ethers with the proper degree of substitution, and especially methylcellulose, can be effectively employed not only as a masking composition but also as a dye vehicle and a dye transfer medium, and that when applied to an anodized aluminum surface and heated to the gelation temperature of the methylcellulose, it will dye the covered areas with the dye carried by the methylcellulose composition. This feature of the invention can be employed, for example, to dye an anodized surface of an aluminum article, without employing the usual large dyeing bath. In accordance with this feature of the invention, a water solution of proper cellulose ether with the proper degree of substitution, and especially methylcellulose, containing a dye, is applied to the anodized surface of the aluminum article by any suitable means, as for example, by spraying, painting, roller coating or silk screening. The resulting coating is then heated by infrared heat or radiant heat or any other suitable form of dry heat to the gelation temperature of the cellulose other. This dry heating operation will cause the dye in the coating to penetrate to the covered area of the aluminum article at elevated temperature and to dye said area with sharp delineation. This process, among other advantages, serves to dye the aluminum article without the use of dye baths.

The coating of gelated aqueous solution of cellulose ether on the anodized surface of the aluminum article, with or without the dye therein, can be employed to seal the anodized surface without the use of the usual hot sealing baths. For that purpose, the coating of gelated aqueous solution of cellulose ether is heated by dry heat, such as infra-red or radiant heat to a sealing temperature, which should be above 170 F. and preferably close to 212 F. The layer of Water in the coating adjacent to the anodized surface heated by this action heats the anodized aluminum surface and supplies the water necessary to change the aluminum oxide to aluminum oxide monohydrate.

This feature eliminates hot water sealing tanks, and when the solution of cellulose ether is employed with a dye, the usual rinsing of the dye applied in the usual manner by a dye bath is eliminated.

The cellulose ether coating, with or without the dye, on the aluminum article treated and sealed as described, can be employed to protect the coated surface of the article during storage and/ or transportation against damage and when the protective function of the coating is no longer required, it can be washed away with water at room temperature, leaving behind a sealed surface, dyed or undyed.

The present invention has utility, even though the cellulose ether coating, with or without the dye, is gelled by means of a hot liquid'bath. The heating of the coating containing a dye by means of a liquid'bath to a temperature above the gelation point but below the sealing temperature, will gel the coating and at the same time, will cause the dye from the coating to penetrate into the aluminum surface and dye it. Also, after the coating has been washed off with cold water, the anodized surface, whether dyed or undyed, can be sealed in a hot liquid bath. a

The property of certain cellulose esters, and especially methylcellulose described, is utilized in accordance With another embodiment of the present invention to produce a multi-dyed pattern on the anodized aluminum surface. In accordance with this embodiment of the invention, the methylcellulose is formed into a water solution in the manner described above but containing a dye and is applied in a predetermined pattern to a part of the anodized surface of the aluminum article, as for example, by rolling, spraying, painting, printing, or silk screening, to form a coating thereon. This coating is then heated at least to the gelation temperature of the methylcellulose, either by dry heat as described or by a hot water bath, to form a water-insoluble mask on the anodized surface and to dye at the same time the coated part of the anodized surface. While the methylcellulose coating on the anodized surface of the aluminum article is in this protective gel form, an uncovered part of the aluminum article is dyed a different color in a dye bath. The later dye bath may be employed not only as a means for dyeing the uncoated areas of the surface, but also as a' heating means for gelling the methylcellulose solution into insoluble form and for causing the dye carried by said solution to dye the coated area. As an alternative, the heating bath may be merely hot water to gel and dye the coated areas, and the dye bath may be separate from the heating bath and may be applied "after the coating has been gelled and the coated areas have been dyed. In the latter alternative, the heating bath is at least at a temperature in the gelation range of the methylcellulose, i.e. above about 115 F. but 'below the sealing temperature of the aluminum, i.e. below 170 F., and the dye bath is at the necessary dyeing temperature which is usually above 115 F. and should be below the sealing temperature. Where the dye bath also serves as a gelling bath for the methylcellulose coating, the dye bath is at least ata temperature in the gelation range of the methylcellulose, i.e. above about 115 F. but below the sealing temperature of the aluminum, i.e. below 170 F.

Washing in cold water removes the methylcellulose gel, leaving the aluminum dyed in two predetermined colored patterns. Sealing in hot water at a temperature above 170 F. follows.

As already described, the proper cellulose ether, and especially methylcellulose, can be applied in any suitable manner, as for example, by printing, rolling, spraying or silk screening, the viscosity of the methylcellulose solu tion employed depending on the manner of application' For example, for spraying or silk screening, the methylcellulose solution will be in fluid state, while for printing 7 7 tween 1.40 and 2.10 may be used for the purpose of the present invention. Methylcellulose having a degree of substitution of between 1.60 and 2.10 gives the firmest gel and isthe most desirable. Methylcellulose is sold commercially in different molecular weights and is rated commercially according to the viscosity of the solution when employing a predetermined concentration of meth* ylcellulose. For example, Methocel, a methylcellulose sold by Dow Chemical, is classified according to the viscosity of the solution when a 2% concentration of the methylcellulose is employed. To illustrate, a Methocel 25 cps. (centipoises) would produce a solution of 25 cps. when employing a concentration of 2% methylcellulose. When a 3% concentration of Methocel 2S cps. is used, the absolute viscosity of the solution goes up to approximately 30 cps. and at 6% it goes up to 750 cps. The concentration of methylcellulose employed, therefore, depends on the cps. rating of the methylcellulose, and the viscosity of the methylcellulose solution desired. In any case, it is preferably between 1% and 6%.

In general, as the concentration of the methylcellulose is increased, the gel point will be lowered. 'Also, the higher the viscosity of the methylcellulose employed, the lower the gel point at the same concentration. A change of 2% in concentration can cause a 10 C. drop in the gelation temperature.

Methylcellulose, which is in the form of a powder, can be solubilized easily by first slurrying the powder into 15 to A; of the required amount of water as hot (176 F.) water and then mixing thoroughly to obtain a uniform dispersion. The remaining water is then added as cold water and stirred until smooth. If the methylcellulose solution is to "be employed also as a dye vehicle, the dye can be added either after the solution has been completely formed, or if in a dry state, it may be dry blended with the methylcellulose before mixing them in the liquid phase. If desired, methylcellulose can be dispersed directly into cold water, but it may require a small amount of wetting agent.

It the methylcellulose solution is to serve as a dye vehicle, the concentration of the dye in the solution may be 1 to 5% according to the character of the dye and the intensity of the color desired in the aluminum surface. Any suitable dye which is now employed for dyeing anodized aluminum surfaces can be employed. The dyes, for example, may be acid dyes, mordant dyes, direct dyes and natural dyes. They may belong to various classes, such as azo, including monoazo, diazo, and triazo, triphenylrnethane, xanthene, anthraquinone, oxazine, nitroso, and phthalocyanine.

Dye baths for dyeing anodized aluminum surfaces are usually operable at a pH of 4 to 8. Methylcellulose is compatible and stable at a pH of 2 to 12, so that the methylcellulose will maintain its integrity in the presence of the dye bath.

The following examples illustrate a certain way in which the principles of the invention may be applied but are not to be construed as limiting the broader aspects of the invention. a

Example 1 Make a 6% water solution of Methocel MC 25 cps.

technical grade having 1.64-2.03 degree of substitution in the manner described above to produce a viscous liquid having almost a paste-like consistency. This paste will have a gelation temperature of approximately 115 F. The paste is applied to a predetermined area on the anodized surface of an aluminum product and the product is immersed in a dye bath at a temperature of 150 F. for about four minutes. The dye bath may be the usual one ordinarily employed in coloring anodized aluminum. For example, it may be an acid dye and specifically an Aluminum Copper BF dye, the concentration of dye in the bath being 3%. This operation will dye the exposed anodized surfaces of the aluminum article, and cause the methylcellulose coating to gel and become insoluble, so that it masks and protects the covered area of the aluminum against the action of the dye bath. The dyed aluminum article is then removed from the dye bath and washed in cold water to dissolve the methylcellulose from the surface. The anodized surface of the aluminum product is then sealed by heating in Water at a temperature of 210 F. for minutes.

Example 2 The methylcellulose solution described in Example 1 but containing 3% of a suitable dye, as for example, a Cl. Acid Red 183 is applied to a predetermined part of the anodized surface of an aluminum article in the form of a thick coating, and the aluminum article so coated is immersed in a dye bath containing 3% 0.1. Direct Blue 71 at a temperature of 150 F. for about 5 minutes. article is then rinsed in cold water to wash off the methylcellulose coating leaving behind a red colored area of the aluminum surface where the methylcellulose coating had been applied and a blue colored area beyond the coated or masked area. The two-colored aluminum article can then be sealed in water at a temperature of 210 F.

Example 3 The methylcellulose solution described in Example 1 and containing 3% of a suitable dye, as for example, a Cl. Red 183 is applied to a predetermined part of the anodized surface of an aluminum article in the form of a thick coating, and the aluminum article so coated is subjected to the dry heat of infra-red rays to a temperature of about 150 F. for about 5 minutes. The article is then subjected to the same infra-red rays but at a temperature of about 212 F. for about 10 minutes to seal the dyed surface. The methylcellulose coating is then washed off with water at room temperature.

While the invention has been described with particular reference to specific embodiments, it is to be understood that it is not to be limited thereto but is to be construed broadly and restricted solely by the scope of the appended claims.

What is claimed is:

1. The method of treating the anodized surface of an aluminum body, which comprises coating said surface with an aqueous solution of a cellulose ether having the properties of being soluble in water at room temperature and of gelling into water insoluble form at elevated temperature, heating the coating formed on said surface by dry heat at least to the gelation point of the cellulose ether, and sealing the anodized surface by heating said anodized surface by dry heat above the gelation temperature of the cellulose ether, While said surface is coated with the gelled cellulose ether.

2. The method of treating the anodized surface of an aluminum body, which comprises coating said surface with an aqueous solution of a cellulose ether having the properties of being soluble in water at room temperature and of gelling into Water insoluble form at elevated tem perature, heating the coating formed on said surface at The O least to the gelation point of the cellulose ether, and sealing the anodized surface by heating said anodized surface by dry heat above the gelation temperature of the cellulose ether, while said surface is coated with the gelled cellulose ether.

3. The method of producing two tones on the anodized surface of an aluminum article, Which comprises coating a predetermined pant of the anodized surface of the article with an aqueous solution of a cellulose ether having the properties of being soluble in Water at room temperature and of gelling into water insoluble form at elevated temperature, subjecting said anodized surface to a dye bath hot enough to gel the cellulose ether and at the same time to dye the exposed part of the anodized surface, and removing the coating formed on said surface from said surface.

4. The method as. described in claim 3, wherein said aqueous solution of cellulose ether contains a dye, and said coating when heated by said dye bath causes the dye in said coating to penetrate into the coated part of the anodized surface.

5. The method of producing two tones on the anodized surface of an aluminum article, which comprises coating a predetermined part of the anodized surface of the article with an aqueous solution of methylcellulose having the properties of being soluble in water at room temperature and a gelling into insoluble form at elevated temperature, subjecting said anodized surface to a dye bath hot enough to gel the methylcellulose and at the same time to dye the exposed part of the anodized surface, and washing oif with Water the coating formed on said surface from the surface at the temperature at which the methylcellulose is soluble in water.

6. The method of producing two tones on the anodized surface of an aluminum article, which comprises coating a predetermined part of the anodized surface of the article With an aqueous solution of methylcellulose having the properties of being soluble in water at room temperature and of gelling into insoluble form at elevated temperature, immersing the coated article in an aqueous dye bath at a temperature in the gelation range of the methylcellulose to cause the coating to gel into water insoluble form and at the same time to dye the exposed part of the anodized surface, and washing oif with water the coating from said surface at the temperature at which the methylcellulose is soluble in water.

7. The method of producing two tones on the anodized surface of an aluminum article, which comprises coating a predetermined part of the anodized surface of the article with an aqueous solution of methylcellulose having the properties of being soluble in water at room temperature and of gelling into insoluble form at elevated temperature, said solution containing a dye, immersing the coated article in an aqueous dye bath having a temperature in the gelation range of the methylcellulose and containing a dye different from that in the methylcellulose solution, (1) to cause the coating to gel into Water insoluble form, (2) to cause the dye in the coating to penetrate into the coated part of the anodized surface and dye the latter part, and (3) to cause the dye bath to dye the uncoated part of the anodized surface, Washing off the coating in water at a temperature in which the methylcellulose is solub-le, and sealing the anodized surface.

References Cited in the file of this patent UNITED STATES PATENTS 2,160,782 M-aasberg May 30, 1939- 2,514,410 Olpin et a1. July 11, 1950 2,778,790 Sobol Jan. 22, 1957 2,812,295 Patrick Nov. 5, 1957 

6. THE METHOD OF PRODUCING TWO TONES ON THE ANODIZED SURFACE OF AN ALUMINUM ARTICLE, WHICH COMPRISES COATING A PREDETERMINED PART OF THE ANODIZED SURFACE OF THE ARTICLE WITH AN AQUEOUS SOLUTION OF METHYLCELLULOSE HAVING THE PROPERTIES OF BEING SOLUBLE IN WATER AT ROOM TEMPERATURE AND OF CELLING INTO INSOLUBLE FORM AT ELEVATED TEMPERATURE, IMMERSING THE COATED ARTICLE IN AN AQUEOUS DYE BATH AT A TEMPERATURE IN THE GELATION RANGE OF THE METHYLCELLULOSE TO CAUSE THE COATING TO GEL INTO WATER INSOLUBLE FORM AND AT THE SAME TIME TO DYE THE EXPOSED PART OF THE ANODIZED SURFACE, AND WASHING OFF WITH WATER THE COATING FROM SAID SURFACE AT THE TEMPERATURE AT WHICH THE METHYLCELLULOSE IS SOLUBLE IN WATER. 